Recent research on polymer materials has focused on the development of a strong polymer material for special purposes, and on its safety. However, increased social awareness worldwide of the environmental problems associated with discarded polymer materials has led to efforts to develop an environmentally-friendly polymer material.
Environmentally-friendly polymers are typically classified as photodegradable and biodegradable polymers. In general, biodegradable polymer materials have a functional group at their main chain that can be decomposed by microorganisms. Among these materials, much research has focused on aliphatic polyester polymer because it has excellent manufacturing and easily-adjustable decomposition characteristics. In particular, polylactic acid (PLA) is widely used in food packing materials and containers, cases for electronics, and the like, replacing conventional plastics, with a worldwide market of 150,000 tons. Accordingly, polylactic acid resin has been primarily used in disposable products, for example food containers, wraps, films, and the like due to its biodegradable characteristics. Examples of commercially produced polylactic acid include polylactic acid polymers produced by American Natureworks LLC, Japanese Toyota Motor Corp., and the like.
However, since conventional polylactic acid resin lacks formability, mechanical strength, and heat-resistance, it may be easily destroyed when made into a thin film. In addition, since it has low temperature resistance, a molded product made thereof may be distorted at a temperature of 60° C. or higher.
In order to solve these problems, polylactic acid resin has been blended with conventional petroleum-based thermoplastic plastics, for example polycarbonate resin, polyamide resin, acrylonitrile-butadiene-styrene (ABS) resin, polyacetal resin, and the like.
Japanese Patent Laid-Open Publication No. 1999-279380 and No. 2006-070224 disclose a method of increasing heat-resistance of polylactic acid resin by using a polylactic acid-ABS resin composition, and Japanese Patent Laid-Open Publication No. 2006-143772 and U.S. Pat. No. 5,272,221 disclose a method of enhancing biomass by using a polylactic acid-polyamide resin composition. In addition, Japanese Patent Laid-Open Publication Nos. 2003-147180 and No. 2003-138119 disclose a method of increasing heat-resistance and the like by using a polyoxymethylene-polylactic acid resin composition.
However, when polycarbonate resin is included in a blend in an amount of 50 parts by weight or less, there is a problem in that polylactic acid forms a continuous phase and polycarbonate resin forms a dispersed phase due to the relatively low viscosity of the polylactic acid during the compounding process. When polylactic acid forms a continuous phase, the resin composition may not exhibit improved properties such as thermal stability, hydrolysis resistance, and the like. Accordingly, there is no significant advantage of blending a polycarbonate resin with polylactic acid resin.
Japanese Patent Laid-Open Publication No. 2006-321988 prescribes the viscosity of a polyolefin to form a continuous phase when it is blended with polylactic acid. However, it does not specifically disclose a method of improving the viscosity of polylactic acid.